The purpose of this investigation is to describe the quantitate the capillary-fiber architecture of skeletal muscle and myocardium in normoxic animals and in animals exposed chronically to hypoxia and cold, alone or combined, and to ascertain how these changes affect the transport of oxygen. These studies will be conducted on sedentary and on exercised animals. Histochemical technqiues will be used to visualize with the aid of sterological technqiues. These data will be correlated with cardiopulmonary data to determine the role of the cytoarchitecture in the transport of oxygen at the level of the tissues. Adaptation in the anatomical diffusion capacity of lung, resulting from growth under these chronic stresses, will be assessed using morphometric technique on lung tissue prepared for light and electron microscopy.